Even though prior art heating and cooling apparatus had fuel valve controls, plenum air temperature sensors, air circulating fans, induced draft blowers for the exhaust gases of a furnace, ignition and flame sensor apparatus for proving that the ignition of the fuel in the burner takes place, and many other parameter sensors, all of which were a part of a control system for a furnace or air conditioning compressor supplying heated or cooled air to a space in which a thermostat was contained, there has been a continual need for improvement in such control systems. With the advent of increased energy costs, an even greater demand has been shown for more efficient heating and cooling apparatuses and systems, especially for homes and dwellings wherein an individual furnace and air conditioning supplies the heated or cooled air to the home as required by a space thermostat.
Coincidental with the increased cost of energy, the advent of low cost microprocessors has made it possible for the gathering of parameter data and the control of various components of a control system in many new manners which provide the long-awaited increased efficiency and thus cost saving in the operation of a furnance and air conditioning apparatus.